By Joanna Stern

Cheap plastic and cluttered software.

You will find some variation of those two criticisms in my coverage of every Samsung Galaxy S smartphone to date.

But not this time. The Galaxy S6 and the Galaxy S6 Edge are Samsung's attempt to finally convince the world (or at least snooty phone reviewers like myself) that it has design chops akin to Apple or HTC.

When it comes to its hardware, I'm now a believer. When it comes to its software, I see the efforts, though I'm still not totally convinced.

Classy Hardware

The S6 and the S6 Edge, which will be available in April in the U.S., are the most beautiful phones Samsung has ever made. Now, I realize that may not be saying much given the company's long history of unspectacular slabs. Still, by making a few strategic sacrifices, Samsung built a pair of phones that can go head to head with the iPhone 6 and HTC One on any catwalk.

(Although, in more places than one you can see the Apple influence: The circular speaker slots on the bottom and the rounded edges are very reminiscent of the iPhone 6.)

There is no more plastic. Anywhere. The frame surrounding the screen is made out of aluminum and the back consists only of a smooth piece of shiny and glossy Gorilla Glass. That creates for a reflective device that catches the light in unusual ways. The gold and emerald versions, especially, sparkle like crystals when rotated.

The S6 Edge is set apart only by sloped edges that run down both sides of its 5.1-inch, 2560x1440 display. Like the Galaxy Note Edge, you can turn those into an info strip of information, and control the phone with edge swipes. But I'd probably disable all that; more than anything else, the curves add to the gorgeous aesthetic.

Just don't drop these new phones in the toilet. Last year Samsung may have tried to sell you a waterproof Galaxy, but this year it would rather sell you a beautiful one.

Seriously, I haven't wanted to hold a Samsung phone this badly since the 2006 BlackJack. Both new phones rest comfortably in my hand, but that glass coating collects more fingerprints than the FBI. You'll be rubbing the phone on your pants to clean it off a lot.

Where you do actually want to put your fingerprint now is on the improved sensor in the home button. Instead of having to swipe down you can just place your finger on it. It logged me in within two seconds time. With that and new NFC and MST payment technology in the phone and Samsung's new acquisition, it seems to be putting on the gloves to take on Apple Pay.

On the back of the S6, you'll find the heart rate sensor and a protruding camera. The new 16-megapixel sensor, up from 13 in the S5, bulges quite a bit, though is said to take better low-light photos. (We haven't yet been given a review unit to put through our battery of tests.) With two taps on the home button, the camera is also now quicker to launch. The phone itself is a performance beast: It now avilable with a octo-core processor and 3GB of RAM.

Improved Software

Samsung says it put that same design effort into improving its modified Android OS and apps. The settings menu has been streamlined and the core apps--email, calendar, S Health, etc.--have been polished up with cleaner styling and a greater use of white space. The phone also isn't as littered with preloaded apps. I'll give a pass to the preinstalled folder containing Microsoft's One Drive, One Note and Skype, since those are actually useful.

Still, a lot of Samsung's typical software tomfoolery lives on. The apps are redesigned--so why do the cheap-looking cartoony home screen icons remain? Also lingering are Samsung's own none-too-useful Galaxy App Store and its MyMagazine news pane. And there's still a Samsung promotional widget on the homescreen.

Samsung's software isn't all that bad anymore, but it isn't all that good, either. And it's certainly not as great as what you get from Google's insanely clean and eye-pleasing Android 5.0 Lollipop. Samsung told me it is working more and more with Google but it still want to maintain its own design identity. Excuses aside, the software just doesn't match the elegant hardware.

The S6 also doesn't push ahead in other areas, or add any features to combat our biggest mobile annoyances. Other than built-in wireless charging (wireless pad sold separately) and faster recharge times, it doesn't address the nagging issue of battery life. Yes, Samsung says it should last a power user most of the day, but for the first time in Galaxy S history, the battery is no longer removeable. There's no MicroSD card slot, either--an omission guaranteed to cause some outrage.

In a time where Samsung is struggling to keep up with competitors, losing those very things that set it apart from the iPhone and others could hurt more than it helps. But beauty always has its price.

Write to Joanna Stern at joanna.stern@wsj.com and at @JoannaStern on Twitter.

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